1. Technical Field
The present invention generally relates to pneumatic tires and, more particularly, to a pneumatic tire having a multiple element bead assembly that minimizes the cord force change under loading in the lower sidewall. Specifically, the present invention relates to a pneumatic tire having an axial inner bead filler element and an axial outer bead filler element that are both disposed outside the ply of body cords allowing the ply of body cords to be disposed against itself immediately above the bead core of the bead assembly. The position of the turn up portion decreases the lower sidewall cord tension variation which reduces flat spotting.
2. Background Information
One common carcass structure for a pneumatic tire includes a ply of main body cords that extend between a pair of bead assemblies. The body cords may extend radially or at a bias between the bead assemblies. Each bead assembly typically includes a loop-shaped bead core fabricated from a plurality of relatively stiff metal wires. Each bead assembly also typically includes a bead filler fabricated from a stiff rubber material. The bead filler is disposed radially above the bead core construction and fills the space between the main portion of the ply of body cords and the turn up portion of the ply of body cords. The shape and material of the bead filler has been altered in numerous prior art applications to provide different characteristics to the pneumatic tire.
The art recognizes that tire carcass design can influence the amount of flat spotting experienced by a tire when the tire is in use on a vehicle. Carcass designs that include turn ups disposed on the opposite side of the bead filler will experience different forces in the main body cords compared to the turn up portion. This is known as cord force variation. For instance, the turn up portion of the body cord may experience a decrease in tension while the main body cord portion experiences an increase in tension. The magnitude of the difference is proportional to the spacing between the main body cord portion and the turn up portion. The difference in these forces contributes to flat spotting. In some applications, the amount of flat spotting is to be reduced and the art desires a carcass structure that helps to reduce the amount of flat spotting.
In view of the foregoing, an aspect of the present invention is to reduce the amount of flat spotting in a pneumatic tire by improving the carcass design. In particular, the invention improves tire flat spotting by providing a bead assembly that has bead filler elements disposed outside the body cords so that the turn up portion of the ply of body cords may be disposed immediately back against the main portion of the ply of body cords above the bead core. This carcass structure reduces cord force variation around the tire under vertical load and decreases the flat spotting retained by the tire.
In another embodiment of the invention, a reinforcing ply is wrapped around the bead filler elements to further increases the stiffness of the lower sidewall. In a further embodiment, a bead filler element is disposed inside the body cords so that air pockets are not formed in the carcass during the manufacturing process.